The present invention relates to an ultrasonic wave diagnostic apparatus for medical diagnostic applications whereby a beam of ultrasonic waves is generated by an array of transducer elements, with beam control being performed using a plurality of values of weighting data, and in particular to an apparatus whereby the number of components required to produce such weighting data is reduced.
When such an ultrasonic wave diagnostic apparatus transmits an ultrasonic wave beam to the interior of a living body, ultrasonic wave echoes which are reflected from the body differ in amplitude in accordance with acoustic impedance presented to the ultrasonic waves as they pass through the body. Data concerning the living body can thereby be derived by scanning the ultrasonic wave beam, and this data can then be used to produce a display image representing a cross-section of the body. Furthermore, by detecting frequency deviations of the ultrasonic wave echoes it is possible to obtain data concerning blood flow. Such a diagnostic apparatus is widely used in the field of medicine. Generally, scanning of the ultrasonic wave beam is executed by using an in-line array of piezoelectric electro-acoustic transducer elements, referred to for brevity hereinafter as piezoelectric elements. Respectively different delay times are applied to pulse-form drive signals which are supplied to the respective piezoelectric elements, for thereby controlling the direction of transmission of the ultrasonic wave beam. In addition, by applying respectively different delay times to the echo signals which are received by the piezoelectric elements and by adding the resultant signals, the directivity of the received signals is controlled. In this way, the direction of the ultrasonic wave beam and the transmit/receive position is altered each time a transmitting/receiving operation is executed. The directivity of an ultrasonic wave beam produced in this way is such that in addition to a main lobe at the beam center, side lobes are produced which exhibit a lower level of gain than the main lobe. Due to mingling of data from these side lobes with the data from the main lobe, deterioration of image quality occurs. As a countermeasure against this, it is possible to lower the channel gain in accordance with distance of a channel (i.e. of a piezoelectric element) from the center of the piezoelectric element array, during at least transmitting or receiving, by deriving respective values of weighting data for the channels and controlling the channel gain in accordance with these data. This enables the side lobe level to be considerably reduced. Such selective modification of channel gain can be performed either by controlling a drive circuit which generates drive signals that are applied to the electro-acoustic transducer elements, such as to selectively reduce the drive signal level, or by controlling the amplification applied to the received ultrasonic wave echoes (e.g. by employing variable gain amplifier circuits for receiving), or by applying such control during both transmitting and receiving. However in the prior art, it has been necessary to apply such control to every channel of the drive circuit or the receiving amplifier circuit, and moreover to provide separate data conversion means (e.g. D/A converters etc.) to produce respective control data for each of the channels, so that a substantial number of additional components are required.
In order to overcome this problem, a method could be envisaged whereby respective sets of mutually adacent electro-acoustic transducer elements are driven in common by respective control signals, i.e. whereby each D/A converter simultaneously supplies identical control data for a specific set of channels. However in practice, as described hereinafter, such a method is not capable of providing a sufficiently high degree of side lobe suppression.